fuel blowing back through carbs

Hello..I have a 97 monte carlo 1000, 3 cyl. At the end of last season, I noticed at WOT she would flood out and bog down, couldnt get no more than 20 mph on the water. I pulled the air box off the carbs and started it up..at full throttle fuel stated to blow back up and out of the carbs. Definitely not right. At any other throttle position she runs smooth..no issues..just at full throttle. A buddy of mine said reed vavles could be the cause..any ideas?